Within weeks of each other, two prominent speakers visited the university where I work and made strikingly similar observations. Nadine Strossen, former longtime president of the American Civil Liberties Union, and Geoffrey R. Stone, a renowned constitutional scholar at the University of Chicago, each noted with bemusement that the people whose freedom of speech they had most often labored to protect are now too often its worst enemies. Their careers had begun by defending leftist causes against autocratic rules and institutions, they said, but now involve arguing against the intolerance of those who had typically been allies.

Thank goodness we still have thinkers such as these, ones who are willing to stay engaged with the free-speech debate. The resolute advocacy of people such as Strossen and Stone — invaluable in its credibility and admirable in their courage to express it — is the nation’s best hope to veer away from the new authoritarianism now threatening our democratic system.

No one has stronger credentials. Stone may be America’s most-honored First Amendment authority, the producer of a host of award-winning books and the editor of the Oxford University Press’s “Inalienable Rights” series of works on the topic by other respected authors. Strossen, the youngest person and first woman to head the ACLU when she began her 17-year tenure as president in 1991, has led for decades across virtually the entire spectrum of liberal causes, including abortion rights, affirmative action and marijuana legalization, always from a staunch civil-liberties perspective.

Both grew up defending, as they saw it, the rights of minority groups, anti-Vietnam War protesters and others involved in causes commonly characterized as left-wing. Now, in maintaining their lifelong defense of free expression, these two liberal lions find themselves often aligned with more-conservative camps that might have once represented the opposition. And they are arguing with, occasionally being maligned by, those who fancy themselves today’s leading leftists.

But they are undeterred. A few years ago, Stone led the drafting of a clear and forthright statement in defense of free expression at his university that is so well done that others of us in higher education have labeled it “The Chicago Principles” and adopted it verbatim at our schools. Strossen travels and lectures and recently published a book for the Oxford series, “Hate: Why We Should Resist It with Free Speech, Not Censorship,” challenging the growing orthodoxy about so-called hate speech.

In a factual and dispassionate way, Strossen’s book demolishes the case for government censorship of hate speech. Laws that attempt to block it are unavoidably overbroad and vague from a constitutional standpoint. Such speech causes little or no real harm, let alone that “serious, imminent” injury that justifies government limitation. There is no justification for having one rule for some identity groups and a different rule for everyone else. Such censorship may imagine that it acts on behalf of minorities, but invariably it endangers minority rights and sooner or later is likely to be used against them.

The principled consistency shown by Stone and Strossen is depressingly rare these days. On both sides of the current political tribal warfare, people have shown themselves quick to abandon supposedly core convictions in rationalizing the actions of their tribe.

It’s hard to name anyone more credible to make the case for free speech than these two, with their unimpeachably liberal records. The same assertions made by people of a different philosophical profile, or by those on the receiving end of today’s repression, are easily dismissed or ignored by the perpetrators and, too often, by the news media.

It’s even harder to think of a more courageous stance on free speech than Strossen and Stone’s. Taking on the dogma of one’s political brethren is tremendously harder than chiming in against traditional adversaries. It’s a familiar truth that the most brutal fights tend to be between close allies; ask pro-life Democrats or “McConnell Republicans.”

The gross excesses of today’s would-be authoritarians, on campus and elsewhere, have started generating an encouraging back pressure from the only kind of voices that are likely to prevail against them. Here and there, academics terrorized in their own classrooms and journalists attacked for unwelcome coverage have begun to speak up.

But all along, a few brave stalwarts such as Geoffrey Stone and Nadine Strossen were standing in the breach, defending the most basic right of a free people. Let’s hope many others will take wisdom from their advocacy and courage from their example.